What authority does a physician have to override a patient’s consent?

The Ontario Court of Appeal provides instructive guidance on the limits of a physician’s authority: The doctor’s authority to make decisions for the patient is necessarily a limited authority. If he knows that the patient has refused to consent to the proposed procedure, he is not empowered to overrule the patient’s decision by substituting his decision for hers even though he, and most others, may think hers a foolish or unreasonable decision. … The doctor has no authority to intervene in the face of a patient’s declared wishes to the contrary. Should he none the less proceed, he would be liable in battery for tortiously invading the patient’s bodily integrity notwithstanding that what he did may be considered beneficial to the patient. [Malette v. Schulman, at p. 10]